This invention relates to apparatus for in situ rejuvenation of asphalt pavement. More particularly this invention relates to a rake associated with such apparatus for initially breaking up an asphalt surface after heating by a heater stage of such apparatus.
Asphalt pavement consists essentially of an aggregate and sand mixture held together with a petroleum based binder, such as tar. With continued exposure to sun, moisture, traffic, freezing and thawing, asphalt surfaces degrade. The degradation is principally in the binder, rather than the aggregate and sand mixture which makes up the bulk of the asphalt. Also, much of the degradation occurs within the top two or three inches of the surface.
Traditionally, worn asphalt pavement was not restored but instead was torn up and replaced with new asphalt. This is a costly approach and creates a problem as to what to do with the torn up pavement. Accordingly, techniques and apparatus have been developed for restoring or rejuvenating the top few inches of an asphalt paved surface.
A typical road resurfacing apparatus has a heater for heating and softening the asphalt surface as it passes along the asphalt surface. Following the heater is a xe2x80x9crakexe2x80x9d or xe2x80x9cscarifierxe2x80x9d which breaks up or xe2x80x9cscarifiesxe2x80x9d the softened pavement. The scarified pavement is generally crushed or xe2x80x9cmilledxe2x80x9d, blended with rejuvenating fluid and optionally additional sand or aggregate and redeposited. The redeposited material is spread out and rolled to create a rejuvenated surface comparable in quality to the original surface before degradation.
Asphalt paved surfaces generally include embedded objects such as access covers and culverts which interfere with the raking operation. As rake designs have heretofore lacked the ability to xe2x80x9cride-upxe2x80x9d over solid objects, it has been necessary to stop raking and raise the rakes until the object was cleared. This necessitated separate treating of the areas around such obstacles and the risk of damaging the rakes if they weren""t raised in time.
It is an object of the present invention to provide a raking device for breaking up a surface which has the capability of riding up over obstacles.
A raking device for breaking up a surface has a plurality of rakes mounted on a rake frame and arranged to produce an upwardly directed resultant force in response to a horizontally directed force arising from encountering an obstruction in a path of travel of the raking device. A rake frame support mounts the rake frame to a rake frame carrier structure and allows controlled movement of the rakes in a vertical direction. A force applicator acting between the rake frame carrier and the rake frame support is provided to apply at least a downward force to the rake. The force applicator is responsive to an increase in the upwardly directed resultant force above a preset amount to allow the rakes to move upwardly in response to the increase in force.
The rake frame support may include at least one linkage member pivotally connected to the rake frame and to the rake frame carrier. The force applicator may include a fluid pressure responsive piston slidably received within a bore and connected to the linkage member to apply the downward force in response to fluid pressure within the bore. The rakes may include a downwardly depending spring secured at a frame end to the rake frame, and a rake tip secured to the rake spring at a tip end of the rake spring, distal the frame end. In use, the frame end leads the tip end.
A fluid pressure supply system connected to the bore through a first fluid conduit may supply the pressurized fluid at a predetermined pressure and flow rate to act on a first face of the piston and cause the piston to exert the downward force. The fluid pressure supply system includes a fluid pressure bleed passage through which a portion of the pressurized fluid being supplied through the first fluid conduit to the bore is continually bled off at a volume flow rate determined by the pressure of the pressurized fluid. The fluid pressure bleed passage allows an increase in the volume flow rate therethrough in response to an increase in pressure as would be occasioned by the piston responding to an increase in the resultant force exerted by the rakes. In this manner, the rakes are enabled to move upwardly in response to an increase in the horizontally directed force.
A plurality of rake frames may be used and the rake frames may be pivotally mounted to allow rocking of the rake frames about a horizontal axis generally parallel to the path of travel of the rakes. The rake frame support may be a parallel bar linkage including at least two laterally extending generally parallel bars pivotably connected, one above the other, to the rake frame at one end and to the rake frame carrier at an opposite end.
Alternatively, the linkage may be a bell crank having a first end pivotably connected to the rake frame, a second end opposite the first end pivotably connected to the force applicator and further pivotably connected between its first and second ends to the rake frame carrier.